Final answer:
The color of the manganate disappears slowly at first and then rapidly as the endpoint is approached in the titration of an acidified solution of ethanedioate with a solution of acidified potassium manganate (VII), due to the oxidation of ethanedioate by the manganate ions.
Step-by-step explanation:
When an acidified solution of ethanedioate (oxalate) is titrated with a solution of acidified potassium manganate (VII), the color of the manganate disappears slowly at first and then rapidly as the endpoint is approached. This is due to the oxidation of ethanedioate by the manganate ions. At first, only a small amount of ethanedioate has reacted, so the color change is slow. However, as more ethanedioate reacts, the manganate ions are rapidly consumed, resulting in a rapid color disappearance. This indicates that the endpoint of the titration is near.